As fossil fuels become depleted and more expensive, the need for cost competitive methods and apparatus for harnessing renewable energy sources increases. The wind was long used for powering sailing ships and windmills, but the advent of steam engines or turbines, internal combustion engines, and gas turbines provided cheaper, more convenient energy sources. Less expensive and more efficient apparatus and methods for utilizing wind power would now be beneficial.
Windmills (or wind turbines) are currently being used to generate electricity and to drive pumps, however the cost to generate electricity with a windmill is still more expensive than the cost of electricity generated from fossil fuels. Windmills have a high capital cost relative to power generated. Wind speed, in general, is higher and more consistent with increasing altitude. There is potential to generate significant power with airborne or aerial apparatus at altitudes above the heights reasonably reachable by ground based windmills.
The challenge with wind power generation is to convert the linear power of the wind to rotary motion to drive an electrical generator or a pump. One known approach to aerial wind power generation is a tethered, aerial windmill. Such aerial windmills can be supported by lighter than air aircraft, such as a blimp, or by lift from airfoil wing structures. These aerial windmills are relatively heavy and require long, heavy electrical cables to transmit the generated power to ground level.
A second known approach to aerial wind power generation is a wind powered element, such as a kite, blimp or airfoil, that is connected to a tow line. The tow line wraps around a reel on the shaft of a ground level power generation device. As the wind powered element is pulled by the wind, the distance from the wind powered element to the shaft increases and the tow line rotates the reel and shaft to generate power. The angle of attack or the shape of the wind powered element is changeable so that the wind powered element can be reeled back towards the ground level power generation device with little power use.
A third known approach to aerial wind power generation is an endless chain of spaced kites linked to the shaft of a ground level power generation device. The kites follow an ascending path and a descending path. The kites are adjustable to provide higher lift while on the ascending path.